The present invention relates to an exposure apparatus such as an exposure apparatus (so-called a stepper) for sequentially projecting and forming an electronic circuit pattern on a reticle surface onto a wafer surface by step and repeat exposure via a projection optical system in the manufacture of semiconductor elements such as ICs, LSIs, and the like, an exposure apparatus (so-called a scanner) for similarly sequentially projecting and forming an electronic circuit pattern on a reticle surface onto a wafer surface by step and scan exposure via a projection optical system, and the like, and so on, and a device manufacturing method that uses the exposure apparatus and, more particularly, to an exposure apparatus used in the manufacture of semiconductor elements, which is hardly influenced by deformation of the main body structure by detecting in advance the relationship between the deformation state of the main body structure and stage precision, and in actual exposure adequately measuring the deformation state and correcting the alignment measurement value and alignment position of a shot in real time, and a device manufacturing method using the apparatus.
The present invention further relates to a high-speed, high-precision alignment stage apparatus which can be suitably applied to, e.g., reticle and wafer moving stages of semiconductor exposure apparatuses, an exposure apparatus having the alignment stage apparatus, and a device manufacturing method of manufacturing a device using this exposure apparatus.
In recent years, as semiconductor integrated circuits such as ICs, LSIs, and the like continue to shrink in feature size, a projection exposure apparatus is required to have further improved image performance, superposing precision, throughput, and the like. The superposing precision can be roughly classified into global components of the shot matrix within a wafer and components within each shot. The former components can be generally subdivided into a wafer shift component, wafer magnification component, wafer rotation component, orthogonality component, and the like. The latter components can be generally accounted for by a shot (chip) magnification component, shot (chip) distortion component, shot (chip) rotation component, and the like. Among these errors, error components produced by deformation of the main body structure have gradually surfaced due to improvements of the apparatus performance.
The error components produced by deformation of the structure are classified into static components reproduced every time after wafer and reticle stages move, and dynamic components such as heat, repulsive force due to step and scan exposure, and the like, which are hard to reproduce.
In order to remove these error components, conventionally, the rigidity of the main body structure is increased; a structure which does not deform even when an external force is slightly applied to the structure, or a structure which does not follow disturbance vibrations due to raised natural frequency is exploited. However, as the rigidity of the main body increases, the weight increases accordingly, and a design that can attain both a weight reduction and high rigidity becomes hard to achieve. When a product is designed in consideration of only high rigidity of the main body, evidently the weight of the main body becomes large, and the obtained product is hard to handle in terms of carrying out/in, installation, and the like of the apparatus.
As measures against heat that have been conventionally taken, the heat source of the apparatus is cooled, its heat generation amount is reduced, a low thermal expansion material is used in a structure, and so on. However, there are more than one heat source in the apparatus, and it is impossible to cool all these sources. Furthermore, even when measures against heat conduction or transfer from the heat sources are taken, an effective measure cannot often be taken for radiation, and thermal influences remain unsolved. Also, the use of a low thermal expansion material in the structure results in higher costs than a normal material, and yet the thermal influences of the heat sources cannot be perfectly removed.
As described above, deformation factors of the main body include dynamic factors such as vibrations, forces, and the like, and thermal factors.
In the former factors, dynamic and static deformations attributed to the repulsion forces of the stages that support the main body structure, and dynamic and static deformations caused by a vibration control/vibration reduction device used for the purpose of controlling vibrations of the main body upon driving of the stages have large components. Of these components, alignment measurement data, print data, and the like indicate that the deformation component due to the force applied to the main body by the vibration control/vibration reduction device to control vibrations of the main body is by no means negligible. Since this deformation component is inevitable in terms of the function of the vibration control/vibration reduction device as long as the stages are driven, it is impossible to set the deformations of the main body structure zero.
The latter factors include changes in ambient temperature, changes in temperature of various heat sources, and the like. Especially, a non-steady process from when the thermal equilibrium state is broken until the thermal equilibrium state is reached again is important for the thermal factors. Since it is impossible to perfectly recognize the thermal behaviors of the individual heat sources and a cooling source such as air in the apparatus, such a non-steady process is produced more or less as long as the apparatus is in operation and processing wafers. Hence, it is impossible to set deformations of the main body structure arising from thermal expansion or shrinkage zero.
On the other hand, alignment stage apparatuses used in semiconductor exposure apparatuses are required to have high alignment precision in order to mount position control targets such as wafers and reticles, and thus widely adopt a stage position measurement means using a combination of a high-resolution laser interferometer and laser mirror.
However, since the position control point and position measurement point do not coincide with each other, deformations arising from changes in temperature and changes in stress cause position measurement errors.
To solve this problem, Japanese Patent Laid-Open No. 4-291910 discloses a method of correcting variations in distance between the position control point and position measurement point. More specifically, as shown in FIG. 26, variations in distance between a laser mirror 2101 as a position measurement target and a wafer 2102 as a position control target are measured by an electric micrometer 2106, and the measurement values are added to an alignment laser target value.
Even this method cannot correct measurement errors produced by deformation and inclination of a fixing jig 2105 for fixing the electric micrometer 2106 to a top table 2104. That is, since measurement errors cannot be completely corrected as far as an additional critical dimension measurement sensor is used, variations in distance between the position control point and position measurement point must be accurately corrected without using any additional critical dimension measurement sensor.
Of these errors, measurement errors due to changes in temperature can be prevented by using a low thermal expansion material, a temperature adjustment device, and the like. However, high stage speeds for a short moving time increase measurement errors due to elastic deformation, so that demands have arisen for correction of variations in distance due to elastic deformation of the stage.
It is still another object of the present invention to correct alignment measurement errors, focus measurement errors, stage position measurement errors, and the like arising from elastic deformation of a projection main body structure in real time in consideration of the fact that the elastic deformation and measurement errors due to the elastic deformation represent the linear sum of operating forces which cause the elastic deformation.
It is still another object of the present invention to accurately correct variations in distance between the position control point and position measurement point due to elastic deformation of the stage.
It is an object of the present invention to attain accurate alignment irrespective of deformations of the main body structure in consideration of the conventional problems. It is another object of the present invention to improve exposure precision of an exposure apparatus without impairing the function of the vibration control/vibration reduction device.
In order to achieve the above object, according to the present invention, even when the structure has deformed, the deformation is measured, and alignment data is adequately corrected based on the measurement result, in place of the effort of making strains or distortions (deformations) of the main body structure due to dynamic factors such as vibrations, forces, and the like, and thermal factors close to zero.
More specifically, according to the present invention, an exposure apparatus, which comprises a substrate stage for holding and moving a substrate, position measurement means for measuring a position of the substrate stage, and control means for performing drive control of the substrate stage to align the substrate on the basis of the measured position, aligns the substrate and a master plate, and forms a pattern on the master plate on the substrate by exposure, comprises strain measurement means for measuring strain of a structure to which the position measurement means is fixed, and the control means aligns the substrate by the drive control of the substrate stage in consideration of the measured strain.
Also, according to the present invention, a control method for an exposure apparatus, which comprises a substrate stage for holding and moving a substrate, position measurement means for measuring a position of the substrate stage, and control means for performing drive control of the substrate stage to align the substrate on the basis of the measured position, aligns the substrate and a master plate, and forms a pattern on the master plate on the substrate by exposure, comprises the strain measurement step of measuring strain of a structure to which the position measurement means is fixed, and the control means aligns the substrate by the drive control of the substrate stage in consideration of the measured strain.
Furthermore, according to the present invention, a device manufacturing method for aligning a substrate held on a substrate stage by measuring a position of the substrate stage using position measurement means and controlling the position of the substrate stage based on the measured position, and for forming a pattern on a master disk onto the substrate by exposure, comprises the steps of: measuring strain of a structure to which the position measurement means is fixed; and aligning the substrate by the position control of the substrate stage in consideration of the measured strain.
In order to achieve the other object, according to the present invention, in an exposure apparatus which comprises a projection optical system, a substrate stage which is movable in a direction perpendicular to the optical axis of the projection optical system while carrying a substrate, a main body structure for supporting the projection optical system and substrate stage, and a vibration reduction device for supporting the main body structure and reducing vibration from a floor, when the substrate stage is aligned to sequentially move the substrate set on the substrate stage in turn to a plurality of predetermined shot positions, a force that the vibration reduction device imposes on the main body structure is measured, and an alignment error and/or stage alignment data are/is corrected on the basis of the measurement result. After the substrate stage is aligned to each shot position of the substrate, the circuit pattern on a master plate is illuminated with illumination light of a predetermined wavelength, thereby projecting and forming by exposure the circuit pattern on the substrate on the substrate stage via the projection optical system.
According to the present invention, a control method for an exposure apparatus, which comprises a projection optical system, a substrate stage which is movable in a direction perpendicular to an optical axis of the projection optical system while carrying a substrate, a main body structure for supporting the projection optical system and the substrate stage, a vibration reduction device for supporting the main body structure and reducing vibration from a floor, and control means for aligning the substrate stage to move the substrate mounted on the substrate stage in turn to a plurality of predetermined shot positions, illuminating a circuit pattern on a master plate with illumination light of a predetermined wavelength after the substrate is aligned to each shot position, and projecting and forming the pattern by exposure onto the substrate on the substrate stage via the projection optical system, comprises the measurement step of measuring a force that the vibration reduction device exerts on the main body structure, and the correction step of correcting the aligned position of the substrate stage on the basis of a measurement result at the measurement step.
Also, according to the present invention, a device manufacturing method which uses a projection optical system, a substrate stage which is movable in a direction perpendicular to an optical axis of the projection optical system while carrying a substrate, a main body structure for supporting the projection optical system and the substrate stage, and a vibration reduction device for supporting the main body structure and reducing vibration from a floor, and which aligns the substrate stage to move the substrate mounted on the substrate stage in turn to a plurality of predetermined shot positions, illuminates a circuit pattern on a master plate with illumination light of a predetermined wavelength after the substrate is aligned to each shot position, and projects and forms the pattern by exposure onto the substrate on the substrate stage via the projection optical system, comprises the measurement step of measuring a force that the vibration reduction device exerts on the main body structure, and the correction step of correcting the aligned position of the substrate stage on the basis of a measurement result at the measurement step.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.
According to the present invention, an exposure apparatus, which comprises a projection optical system such as a projection lens for forming an image of a pattern formed on a master plate such as a reticle, a substrate stage for holding and moving a substrate to be exposed such as a semiconductor wafer to an imaging position, position measurement means for measuring a position of the master plate or substrate or relative positions of the master plate and substrate, alignment means for moving the master plate or substrate on the basis of a measurement value of the position measurement means to adjust the position or relative positions, a main body structure for holding the projection optical system, the substrate stage, and the position measurement means, and a support base for supporting the main body structure, comprises means for measuring a variation amount of a principal force acting between the main body structure and the support base or a physical quantity proportional to the variation amount, and correction means for correcting a measurement value of the measurement means using a correction vector obtained by multiplying the measurement result of the measurement means by a predetermined coefficient matrix.
In preferred embodiments of the present invention, the measurement means is a stage position measurement device for measuring a position of the substrate stage, a focus measurement device for measuring a shift in position or posture of a substrate surface with reference to the imaging position, an alignment scope for measuring an alignment mark on the substrate so as to superpose a new pattern on a pattern which has been printed on the substrate surface, or the like. The alignment scope is a TTL on-axis alignment scope for measuring relative positions of alignment marks on the master plate and substrate using light passing on an optical axis of the projection optical system, a TTL off-axis alignment scope for measuring the relative positions of the alignment marks on the master plate and substrate using light passing off the optical axis of the projection optical system, an off-axis alignment scope for measuring the position of the alignment mark on the substrate outside the projection optical system, a reticle alignment scope for measuring a position of a reticle using a mark on a reticle as a master plate, or the like. To align the reticle, the alignment scope further comprises a reticle stage for holding and moving the reticle.
The predetermined coefficient matrix is estimated by measuring by the measurement means the position of the substrate on the substrate stage aligned and controlled to keep a position and posture constant, at the same time applying a forced operating force to respective portions for supporting the main body structure, and regressively analyzing a variation amount of a measurement value of the measurement means with respect to variations in the forced operating force.
Also, according to the present invention, a stage apparatus comprises a stage for holding and moving an object, stage position measurement means for measuring a position of the stage, a sensor for measuring a variation amount of a principal force acting on the stage or a physical quantity proportional to the variation amount, and means for correcting a measurement value of the stage position using a correction vector obtained by multiplying a measurement result of the sensor by a predetermined coefficient matrix.
The stage position measurement means may comprise a laser interferometer and a reflecting mirror.
In general, the apparatus further comprises position measurement means arranged in addition to the stage position measurement means, and the predetermined coefficient matrix is obtained by regressively analyzing a variation amount of a stage drive force of each axis when the stage is moved or a physical quantity proportional to the variation amount, and a difference between measurement values of the position measurement means and the stage position measurement means.
The sensor can be either one of means for monitoring a current value of a motor for driving the stage and a load cell or strain gauge arranged at a portion where a drive repulsion force of the motor acts.
Further, according to the present invention, there are provided an exposure apparatus comprising the stage apparatus and means for exposing a wafer or reticle mounted on the stage apparatus, and a device manufacturing method comprising the step of manufacturing a device using this exposure apparatus.